A major theme of this project is understanding the causes and conditions that lead to a state of chronic up- regualtion of pro-inflammatory process in aging that are the backround within which neurodegeneartive disease occurs. We have demonstrated that loss of the chemokine fractalkine (FKN) is an early event in brain aging and that this precipitates a bias towards pro-inflammatory signals such as ILI3 and TNFa. Fractalkine (CX3CL1) is expressed in neurons and the receptor (CX3CR1) is on microglia. Ligation of CX3CR1 results in down regulation of 11-1 , TNF? and other pro-inflammatory cytokines. We will examine regulation of CX3CL1 as it is present as both a cleaved soluble form and a membrane bound form. There is evidence that the membrane bound form and the soluble form control different aspects of immune regulation, however this is poorly understood. To address this question we have generated rAAV9 vectors that express 1 )soluble, 2) native and 3) a mutant uncleaved CX3CL1. We will use these unique and novel tools to understand the role these forms of FKN in control of microglial function and its role to regulate neural plasticity measured as neurogensis and long term potentiaion (LTP) and cognitive function in aged mice and CX3CL1 deficient mice to determine if replacement of FKN at an early age (12 months) will lead to king lasting regulation of microglial function and prevent increased innate immune function with age and preverit a loss in neural plasticity and cognitive function. In aim 2 we will examine if neural specific versus astrocyte specific expression of CX3CL1 alters the functional properties. CX3CL1 is normally epxressed in nuerons, hoever under certain conditions it has been observed in astrocytes. In aim 3 we will then look further at the role of CX3CL1 and its receptor as it may interact with Ml and M2 responses to stimuli with age, as we have observed blunted responses to iL4/IL13 in the aged brain. We will examine this in the CX3CR1 null and CX3CL1 null mice as well as normal aged C57BL/6 mice. We will isolate primary microglia for ex vivo cell culture experiments to determine if any changes in regulation of M1 and M2 responses are cell autonomous or non cell autonomous.